Technical Field
The present invention is related to a metal laminate, in particular to adhesive-free metal laminate whose insulating layer is made of polyimide resin.
Description of Related Art
Flexible printed circuit board (FPCB) has been widely used in high-density portable electronic devices due to its flexible features. Traditional polyimide (PI) FPCBs use a thermosetting polyimide resin as insulating layer. An adhesive (such as epoxy) is coating on one side of thermosetting polyimide resin to bond with metal layer (such as copper foil). The product is called single-side metal laminate. If the laminate needs to support more circuits, the adhesive could be coated on both side of the thermosetting polyimide resin to bond metal layer. The product is called double-side metal laminate. However, the adhesive may decrease the flexibility, solder resistance, dimensional stability and limit the thickness of the metal laminate. Also, the adhesive may cause environmental problem.